Ignitron starter



March 18, 1941. R, F. RENNIE IGNITRON STARTER Filed April 19. 1939 www2Re Y

w OM E M mw m W 2 m Y B Patented Mar. 18, 1941 UNITED STATES PATENTOFFICE IGNITRON STARTER Robert F. Rennie, Little Falls, N. J., assignorto Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,a corporation of My invention relates to starting electrodes andespecially to the make-alive type of starting electrode utilized withmer-cury pool devices.

An object of the invention is to provide a make-alive electrode madefrom compressed materials having a uniform shape and uniform sintering.

Another object is to provide a method of forming make-alive electrodesthat can be produced in quantities with uniform characteristics.

Other objects and advantages of the invention Will be apparent from thefollowing description and drawing in which:

Figure 1 is a vieW in front elevation of a discharge tube having amake-alive therein;

Figure 2 is a view mainly in cross-section illustrating one of theinitial steps in forming the make-alive; I

Figures 3, 4, 5, 6, 7 and 8 are views mainly in cross-sectionillustrating subsequent steps in the formation of the make-alive.

The invention relates to the formation of a make-alive and in Figure 1is illustrated a typical discharge tube which utilizes such a makealive.The tube illustrated in Figure 1 has a glass'envelope I0 with a mercurypool II in the lower portion thereof. A contact pin I2 has a connectionI3 to the mercury at I4. At the upper end of the tube is an anode I5. Aconnecting pin I6 at the base of the tube has a connection I'l, and thisconnection passes through the press I8 to an arbor I9 that makes asupporting contact with the shaft or connectying pin upon the lower endof which is the make-alive 2|.

As is well known, this make-alive 2| consists of a high resistancematerial and in operation a voltage is applied to this make-alive, and aseries of tiny sparks or discharges will be created along the lowersurface of the make-alive at the surface of the mercury. Thesedischarges will ionize the mercury vapor and make the tube break down ifa suitable voltage is applied across the anode I5 and the mercury pool II.

45 It is necessary, of course, that the make-alive 2| be of suchcomposition 'as to be able to Withstand the corrosive action of thesetiny discharges for initiating the current. The makealives heretoforeconstructed have been very ex- 50 pensive to manufacture. My inventionprovides a cheaper method suitable for quantity production and at thesame time provides for uniform shape and consistent characteristics ofthe makealive.

The material from which I prefer to construct the make-alive is from to'60% silicon and ythe rest principally silicon carbide or boron carbideor a mixture of both. In place of 60% silicon, ferro silicon may beutilized, or a combination of ferro silicon and silicon. Small amountsof iron oxide such as 1 to 10% may be used. Other silicides, carbides,nitrides, or borides may also be used. I prefer, however, to use ferrosilicon of the 85% grade which consists of FeSiz and free Si. The gradeconsisting of FeSiz and 10 FeSi could be used. The 40% boron carbide(BiC) is preferably of the 320 grain. These percentages may, of course,be varied.

` My tests have especially covered silicon carbide with the remainder ofvarying percentages of 10 to 60% silicon; 10'to 60% ferro silicon of the85% silicon grade; 10 to 60% ferro silicon of the 50% silicon grade; .10to 60% ferro silicon of the 25% silicon grade and 10% cobalt. They havealso covered boron carbide with 10 to silicon, 10 to 60% ferro siliconof the grade; 30 to 60% ferro silicon 0f the 50% grade; 30 to 60% ferrosilicon of the 25% grade, and 10% cobalt. Other proportions included 40%boron carbide, 20% silicon carbide, 40% silicon; 45% boron carbide, 45%silicon carbide, 10% silicon; 40% boron carbide, 50% silicon, 10% ferrosilicon (85% grade); 45% boron carbide, 45% silicon carbon, 10% ferrosilicon (85% grade); 40% boron carbide, 55% silicon, 5% iron 30 and 40%boron carbide, 52% silicon, 8% iron oxide.

The mixture of silicon or ferro silicon and boron carbide is well mixedby ball milling. 'I'he mixture is then ready to be placed in the die. 35Figure 2 illustrates a preferred form of, apparatus for forming themake-alive. This. consists of a die 25 formed as a cylinder with aconical shape desired for the pointed end 22 of the makealiveillustrated in Figure 1. ing of the die continues into a cylindricalopening 21 extending through the remaining portion of the die. In thisopening is located a rod 28. The die and rod are placed in the die block29 which has a cylindricn opening therethrough 4 corresponding with theouter diameter of the die 25 and the desired cylindrical diameter of themake-alive.

For the purpose'of compressing the conical point of the make-alive ashereinafter described, 0 it is desired that the rod 28 in the dieproject a little from -the die and accordingly the die and die block'are. placed on a supporting plate 30 perforated to/accommodate theprojecting portion 3| of the rod. The whole assembly rests` D 'I'heconical open- 40' upon a suitable support 32. The desired quantity ofthe boron carbide,'silicon, or ferro silicon or other mixture, is thenplaced inthe die and die block, as illustrated at 33. The connecting rod20 for the make-alive is then inserted in this mixture. This connectingrod 20 is preferably of molybdenum, and at its lower end is pointed ortapered at 34 to correspond somewhat with the conical taper ,o/f themake-alive.

A plunger 35, having a central opening to accommodate the molybdenum rod29, compresses the mixture 33 as illustrated in Figure 3. At the sametime a press 31 is applied to the upper end of the molybdenum rod 20 topress its lower pointed end down to the desired location within themixture 33. The press and plunger are then removed, and I prefer to turnthe die block 29 upside down upon a lower die block 39, as illustratedin Figure 4. The rod 2l has its projection 3i extending above thesurface of the die block 29.

A plunger 39, having the diameter of the central opening through the dieblock, is then applied to the assembly in this central opening of thedie block. The first contact of this plunger 39- is upon the extension3l of the rod 2l.' The first action will be to compress the tip 40 ofthe boron carbide, silicon, or ferro silicon mixture, as illustrated indotted lines in Figure 4. The plunger 39 will then enter the centralopening of the die block and push out the die 25, rod 28, pressedmake-alive mixture 33 and connecting rod 20 from the die block 29.

The pressed make-alive can then be removed from the die in anyconvenient manner. I have found it convenient to use the apparatus inFig- 6 for this purpose. This apparatus comprises a vise 40 for holdingthe die 25 by means of a screw 4I. The vise is also screw threaded toreceive a turn screw 42 that has a shaft 43 applied against the end ofthe rod 29 and of somewhat smaller diameter. By turning the screw 42with the general pressure, the rod 28 will gently force the compressedmake-alive 33 out of the die.

To obtain a uniform sintering temperature, the starters are buried in apowdery medium that will not sinter together too hard at the temperatureemployed. Silica has been found to answer /,the,purpose. It has beenfound desirable to mix "sorne graphite with the silica to furnish asuitable iiring atmosphere. Fifteen to seventeen per cent. has beenfound to be especially suitable, although this percentage may be varied.

I have also found it advisable to give this mixture a pre-ring'at 1500C.`in hydrogen and then to regrind it before utilizing it to surroundthe compressed make-alives. In Figures 7 and 8 I have illustrated thecombination of the starters and the mixtures in a portion of one type offurnace. The furnace, which may be electrical, is illustrated by thewalls 50 and upon the lower wall is resting the so-called furnace boat5I having the mixture of silica and carbon therein. The

compressed make-alives 33 with their connecting` molybdenum rods 20 areillustrated buried in the mixture.

In Figure 7 is illustrated the first step of prering in air anywherefrom 200 to 600 C. I prefer to preheat at approximately 570 to 580 C. Ifit is desired to reduce the resistance of the nnished starter, thepre-firing should be at higher temperatures than 580 C.

In Figure 8 I have illustrated the second step in which hydrogen isapplied through the rurnace and this hydrogen is preferably at atemperature between 1500 and 1600 C. 'I'he hydrogen is preferably driedover P205 and the gas now is kept preferably as low as possible. about11/2 cubic feet per hour. The firing is preferably of the order of eightminutes.

'I'he boat is then removed from the furnace and the uniformly sinteredmake-alive removed from the silica carbon mixture. After the silicacarbon mixture is removed, the make-alive is then ready for insertion ina discharge device, such as that illustrated in Figure 1, which ofcourse is for purposes of illustration and not to limit the invention.

It is apparent that many modifications may be made in the order of thesteps and the particular shape of the apparatus utilized and also thecomposition of the materials specified without departing from the spiritand scope of the appended claims.

I claim:

l. 'I'he method of making an auxiliary startl ing electrode for contactwith a mercury pool which comprises packing under pressure, a powderedmixture of material with a conductor, burying the packed mixture andconductor in a loose second mixture and sintering the first packed'mixture on said conductor in a gas furnace.

2. The method of making an auxiliary starting electrode for contact witha mercury pool which comprises packing under pressure a powdered mixtureof material with the end of a conductor including the step of forming asubstantially conical tip to said material, burying the packed mixtureand conductor in a loose mixture and sintering the first packed mixtureon said conductor in a gas furnace.

3. The method of making an auxiliary starting electrode for contact witha mercury pool which comprises packing under pressure a'powdered mixtureof material with a conductor, embedding in a powdered mixture diilicultto sinter, providing a suitable hot gaseous atmosphere and uniformly bysintering the packed mixture on the conductor.

4. 'Ihe method of making an auxiliary starting electrode for contactwith a mercury pool which comprises placing material in a die with aconical depression, compressing said material and inserting a conductortherein, removing said compressed material and conductor, embedding themin a mixture difiicult to sinter and sintering said compressed materialon the conductor in a gaseous atmosphere.

5. The method of making an auxiliary starting electrode for contact witha mercury pool which comprises placing material in a die with a conicaldepression, compressing said material and inserting a conductor therein,removing the compressed material and conductor and embedding them in amixture of silica carbon and sintering the compressed material in agaseous furnace.

6. Means for uniformly sintering a. compressed powder on a conductor foran electrode, which comprises an enclosing powdered silica carbonmixture for the electrode, a container for the mixture and a hot gaseousatmosphere to sinter the compressed powder.

ROBERT F. RENNIE.

